HYDRAULIC INVESTIGATIONS. Hi 



3Tor example, in the last experiment, where d is 1, / 4, j^™^!^* 



_ 1 cienu. 



and h 27*1, we have a =z -000025Q, b == ~JTJ^{-~ 7 001S2 W 



516", c == -0001063, ezzbclidzz "22, and v = </ {bh f e % ) 

 — -e— 118*46, which agrees with the experiment within yi^ 

 of the whole. I had at first employed for a the formula 



430 57 1 



1 + 1 2 • d "•" ~J "*" &&/' but * found > that the value, thus 



determined, became too great when rf was about 20, and too 

 small in some other cases. Coulomb's experiments on the 

 friction of fluids, made by means of the torsion of wires, 

 give about '00014 for the value of c, which agrees as nearly 

 with this table, as any constant number could be expected 

 to do. I have however reason to think, from some experi- 

 ments communicated to me by Mr. Robertson Buchanan, 

 that the value of a, for pipes about half an inch in diame- 

 ter, is somewhat too small; my mode of calculation, as 

 well as Dubuat's, giving too great a velocity in such cases. 



If auy person should be desirous of making use of I)u- Assistants t» 

 buat's formula, it would still be a great convenience to be- Dubuat ' s for " 

 gin by determining v according to this method; then, tak- 

 ing b zz » v %. 478 > or rather, as Langsdorf makes it, b rr 



h — v % ' 482 * to P rocee( * m calculating v by the formula v 



zz 148-5 (•<*--) • (^h-HAL* [b+l-6)—°° l )> 

 since this determination of b will, in general, be far more 



accurate than the simple expression b zz — -r and the 



continued repetition of the calculation, with approximate 

 values of v, may thus be avoided. Sometimes, indeed, the 

 values of v found by this repetition will constitute a diverg- 

 ing instead of a converging series, and in such cases, we 

 can only employ a conjectural value of v, intermediate be- 

 tween the two preceding ones. 



Having sufficiently examined the accuracy of my for- The formula 



■aula, I shall now reduce it into English inches, and shall reduced to 



, English roea- 

 a dd sure . 



